In general, since water pipes which are installed at homes, office buildings, or factories, or pipes which transfer various kinds of solutions at factories are inevitably exposed to the outside, in particular, in the air, they may be frozen to burst unless they have heating facilities, respectively.
In high-volume mass production systems of recent frontier industries, temperature, flux or quantity of flow, pressure, level, etc., should be controlled precisely and quickly because they decisively influence upon productivity, quality, etc. Accordingly, a flux transmitter and a pressure transmitter are the most important fields in a manufacturing process. Here, it should be measured along all lines of pipes whether how much flux has flown in the respective pipes or how much pressure has occurred therein. The flux transmitter and the pressure transmitter receive analog signals resulting from the measured fluxes and pressures, in a differential pressure form, and send the received analog signals to a controller to thus control valves.
For this, a heater cable is attached to and installed in an induced pressure pipe line through which flux and pressure of liquid are detected. Then, electricity is supplied through the heater cable, to thus maintain the induced pressure pipe line at 30° C. to 50° C. By doing so, it is required that the induced pressure pipe line should be anti-frozen and accurate flux and pressure should be detected.
According to the conventional art, water pipes which are installed at homes, office buildings, or factories, or pipes which transfer various kinds of solutions at factories, employ various kinds of anti-freezing heaters, in order to prevent the pipes from being frozen to burst.
Korean Utility-model Registration No. 219527 discloses an anti-freezing heater whose heat resistance or durability are excellent and whose cost can be saved. For this, the anti-freezing heater disclosed in Korean Utility-model Registration No. 219527 is configured to includes a heat wire which is connected to an electric power supply cable to emit heat, an inner coat layer made of a silicon material which is coated around the circumference of the heat wire, and an outer coat layer made of a PVC material which is coated to surround the inner coat layer.
The conventional anti-freezing heater disclosed in the Korean Utility-model Registration No. 219527 uses a circular nichrome wire as a heat wire. Since the conventional anti-freezing heater has a small resistance value and emits heat at high temperature, temperature around the heat wire becomes high. Accordingly, there is a defect that the inner coat layer made of the silicon material whose heat resistance is excellent should be necessarily coated thickly around the heat wire. In addition, since the thick outer coat layer surrounds the outer portion of the inner coat layer, and thus the whole thickness is formed of a thick structure of about 3 mm for example, flexibility of the anti-freezing heater is low. As a result, when the anti-freezing heater is wound on a pipe, cohesiveness drops. Further, a heat transfer efficiency that heat emitted from a heat wire is transferred to a pipe becomes low due to a thick coat layer, together with inferiority of the cohesiveness. Still further, since the surface heater uses a nichrome wire which is expensive as a heat wire material, the total cost increases.
In addition, Korean Utility-model Registration No. 293218 discloses a linear heater where a bundle of a conductive fiber and a heat wire are linearly closely adhered and are coated by a coating material, in which the heat wire is wound at predetermined pitch intervals along the outer circumferential surface of the bundle of the fiber.
The linear heater disclosed in the Korean Utility-model Registration No. 293218 uses the heat wire made of a nichrome wire of a fine diameter. Accordingly, the heat wire may be considerably highly cut off. The linear heater is thickly formed of 2 mm thick and 10 mm wide. As a result, when the linear heater is wound on a pipe, cohesiveness drops. Further, a heat transfer efficiency that heat emitted from a heat wire is transferred to a pipe becomes low.
Korean Utility-model Registration No. 137043 discloses a self-controllable polymer heater which is configured to form a conductive coating layer between a conductor and a heating element, in order to play a role of supplementing limited cohesive power between the conductor and the heating element in the conventional self-controllable polymer heater. Accordingly, an increase of an interface resistance is minimized during use between the conductor and the heating element, to thus improve a long-term output stability.
The conventional self-controllable polymer heater disclosed in the Korean Utility-model Registration No. 137043 is thickly formed since it is formed of 3 mm thick and 10 mm wide. As a result, when the self-controllable polymer heater is wound on a pipe, cohesiveness drops. Further, a heat transfer efficiency that heat emitted from a heat wire is transferred to a pipe becomes low.
Meanwhile, Korean Utility-model Registration No. 277428 discloses an anti-freezing heater in which a plug is installed at one side of a cord wire, and a soft insulation coat layer is formed at the other side of the cord wire, a bimetal unit which is an electric current interruption unit is provided in the middle of the cord wire, and then a heat wire containing a heater wire is wound around a water pipe to thus prevent the water pipe from being frozen to burst. Here, the heat wire is wound around the water pipe and the bimetal unit is closely adhered to the water pipe through a space between the wound heat wire.
Most of the above-described anti-freezing heaters use the linear heating element formed of a nichrome wire or heat wire material having a circular cross-section. Accordingly, a thick coating layer is formed on the outer circumference of the heating element, in order to solve a problem due to excess and/or high temperature heat emission. In addition, a thick jacket or cord is disposed between a pair of the heating elements, in order to integrate the pair of the heating elements.
As a result, the whole flexibility of the conventional anti-freezing heater is low. Accordingly, when the anti-freezing heater is wound on a pipe, cohesiveness and workability drop. Further, a heat transfer efficiency that heat emitted from a heat wire is transferred to a pipe becomes low due to inferiority of the cohesiveness and the thick coating layer. Still further, a maintenance cost becomes high, and a manufacturing cost becomes also high.
Meanwhile, a freezer in a refrigerator is provided with a defrost heater such as an electric heater in order to remove frost that is formed on an evaporator. The defrost heater has used a tubular heater such as a sheath or jacket heater that generates heat up to about 600° C. However, since the conventional defrost heater generates heat up to high temperature in common, a safety problem may happen. In addition, since a temperature response performance is low, an electric power supply for the defrost heater is turned off and a compressor operates, immediately after a defrost operation has come to an end. Accordingly, a cooling period of time during which temperature of a refrigerant pipe is low to a point in time at which a refrigerating cycle of a freezer is substantially re-activated, that is, down to 0° C., is long. That is, a temperature response performance of the heater is slow. As a result, the entire defrosting cycle is prolonged. That is, if the defrosting cycle is prolonged, the freezer in the refrigerator cannot be converted into the refrigerating cycle immediately after the defrosting cycle has ended. Therefore, there may be a problem that the freezing performance falls.